I was able to do this by making the following change to wp-comments-post.php
if ( empty($status->comment_status) ) {
do_action('comment_id_not_found', $comment_post_ID);
exit;
} elseif ( 'closed' == $status->comment_status ) {
do_action('comment_closed', $comment_post_ID);
wp_die( __('Sorry, comments are closed for this item.') );
// } elseif ( in_array($status->post_status, array('draft', 'pending') ) ) {
// do_action('comment_on_draft', $comment_post_ID);
// exit;
}
Does that make sense?